1/4 cup + 2 tbs cream cheese (**I've used light cream cheese and it was fine)
1/4 cup softened butter
1 tbs vanilla
1 1/2 cups icing sugar
Soften the cream cheese and butter on the stove. Add the vanilla. Whip in the icing sugar in 2 or 3 instalments.
I found that this was enough to do a crumb coat on the quinoa cake (aka you can barely do one coat and it was full of crumbs from the cake). If I were going to do this for a party or something, I would do a double batch and chill the cake between applications.